The incidence of cancer increases rapidly with age; however, in some cases the rate of growth and tumor spread is slowed with age. The goal of this project is to establish animal models to assess the role of angiogenesis in tumor growth in aging. Extracellular matrix from tumors grown in aged mice contains host factors which inhibit the growth of other transplantable tumors, cause an increase in endothelial cell apoptosis, and fail to promote differentiation of these cells. These studies suggest that a reduced blood supply to tumors may play a role in reduced tumor growth in the elderly.